Herpes simplex virus and other herpes viruses have evolved specialized functions to allow sorting of nascent virus particles to sites of cell-cell contact, thereby promoting rapid and efficient spread of viruses in epithelial and neuronal tissues. Preliminary studies of the HSV US9 membrane protein have suggested that it acts exclusively or predominately in the nervous system to promote virus spread. This proposal seeks to determine how US9 functions in neurons and to investigate the role of US9 in ocular disease. Aim 1 will address the role of US9 in retrograde versus anterograde spread of HSV in neurons, by studying movement of the US9- mutant from the cornea to sensory ganglia and from neuron cell bodies back to the cornea. Aim 2 capitalizes on the notion that US9 functions exclusively in neurons and uses an HSV US9- mutant to address an extremely important question related to HSV keratitis - how HSV antigens reach the stroma before triggering inflammation? It is not clear whether HSV spreads to the stroma from infected sensory neurons or from the epithelial layer of the cornea and the US9- mutant should allow us to distinguish between these two possibilities. Aim 3 will utilize various neurons cultured in vitro in order to characterize the molecular mechanisms by which US9 promotes movement of HSV proteins and cell-cell spread of virus. Together, these studies should provide valuable new information on how HSV interacts with host neurons, and will advance our understanding of HSV keratitis.